Open Data supplied by Natural Environment Research Council (NERC)

Bissett-Berman 9060 Salinity Temperature and Depth

The B-B 9060 STD measured salinity, temperature and depth and whose analogue output was in graphical form. The plots created were of salinity and temperature versus depth which had to be manually digitised.

RRS Challenger Cruise 3/75 CTD Data Documentation

Introduction

Instrumentation

The instrument used was a Bissett Berman 9040 CTD system and the data were logged on a Hewlett Packard 9820 and stored in an integer format. Instrument lowering and raising speeds were between 0.5m/s and 1m/s. An acoustic pinger was placed above the CTD to give an accurate depth measurement, this could then be used to check the CTD pressure calibration. An NIO bottle with reversing thermometers was placed above the pinger, within 2m of the CTD system. A bottle sample was taken at the bottom of the cast providing the temperature and salinity are uniform at that point. If large temperature or salinity gradients were present then the bottle sample was triggered at a suitable site on the upcast. A surface salinity sample was also taken at the start of the dip.

Calibrations and Data Quality

The CTD was not calibrated in the laboratory. The manufacturer's calibration was used and water samples taken to check the calibration and apply corrections where necessary.

Temperature

The manufacturer's calibration was used to convert the raw data to to physical units using the equation below:

Temperature (deg C) = (10**6/Pt -2238.68/55.84) where Pt is the temperature period in microseconds

These values were then plotted against the water bottle (i.e. reversing thermometer) temperatures and a regression line fitted to the data such that:

Temperature(WB) = m x Temperature(CTD) + c

Then the regression coefficients (m and c) were applied to correct the CTD temperature data - these are given in the table below.

Conductivity

The manufacturer's calibration was used to convert the raw data to to physical units using the equation below:

Conductivity (mmho/cm) = (10**6/Pc - 4995)/58.12 + 10 where Pc is the conductivity period in microseconds

The water bottle salinities and corrected CTD temperatures were used to calculate the water bottle conductivity values. These values were then plotted against the CTD conductivities and a regression line fitted to the data such that:

Conductivity(WB) = m x Conductivity(CTD) + c

Then the regression coefficients were applied to correct the CTD conductivity data - these are given in the table below.

Pressure

The depths from the acoustic pinger were noted where the bottle samples were taken and then used to check the calibration of the pressure sensor - unless calibration values were available from the reversing thermometers. The equation below was used to convert the pressure period to physical units.

Pressure = (10**6/Pd - 9712)/0.26267 where Pd is the pressure period in microseconds

A regression fit was carried out using the calibration values and the slope and intercept determined. The pressure values could then be corrected using:

Pressure (CORR) = m x Pressure(CTD) + c

The fit of the CTD data to the water bottle calibration data is given in the table below:

Variable

Slope (m)

Intercept (c)

Standard Deviation

Temperature (°C)

1.0004

0.0540

0.003

Salinity (ppt)

0.8931

3.8041

0.023

Pressure (dbar)

0.5048

-7.2163

7.045

Data Processing

Obvious wild points were edited out of the calibration file and the calibration programs run to obtain values for the slopes and intercepts for temperature, pressure and conductivity. These were then applied to the uncalibrated data. Conductivities were converted to conductivity ratios and then converted to salinities using UNESCO recommended routines and sigma-t was calculated. The data values were then sieved to ensure a minimum separation between pressure values of 1 dbar. The data were then visually inspected and major spikes flagged.

Fixed Station Information

Station Name

DML Malin Head Line

Category

Offshore route/traverse

DML Malin Head Line

The DML Malin Head Line is a survey section crossing the Rockall Trough, west of Scotland. The section starts close to the outcrop of Rockall and heads in a south easterly direction towards Malin Head (County Donegal, Republic of Ireland). The final station is at the shelf edge. The section comprises 15 fixed STD/CTD stations, which were established as part of routine monitoring work west of Scotland by Dunstaffnage Marine Laboratory (DML). The DML Malin Head Line was occupied between the mid 1970s and mid 1990s.

Map of standard DML Malin Head Line STD/CTD Stations

Map produced using the GEBCO Digital Atlas.

The white triangles indicate the nominal positions of each standard Malin Head Line Station. The black circle indicates the location of Rockall.

Fixed Station Information

Station Name

DML Malin Head Line - Station QS

Category

Offshore location

Latitude

57° 23.00' N

Longitude

13° 45.00' W

Water depth below MSL

155.0 m

DML Station QS

Station QS is one of 15 fixed STD/CTD stations crossing the Rockall Trough between the outcrop of Rockall and the shelf edge to the south east. The station was established by scientists at Dunstaffnage Marine Laboratory (DML).

Other Cruises linked to this Fixed Station (with the number of series) - CH10A/75 (1) CH81 (1)